Electrical circuit



April 6, 19 48.

R. ,M. WALKER 2,439,324

ELECTRICAL CIRCUIT Filed Aug. 1,-1945 F|G.l

\l\] NEGATIVE SAWTOOTH u 34 OUT NEGAT I2 35 GATE 1 I3 I 36 v r 2a- POSITIVE SAWTOOTH c /1/1 ouT 0R GROUND FIG.2 POSITIVE r SAWI'OOTH OUT 68L 67 /l/] 47- Clil 70 T v 5| 1 69 \r\| NEGATIVE 49 64 NEGATWE GATE SAWTOOTH INVENTOR ROBERT M. WALKER ATTORN EY fiatented Apr. 6, 1948 ELECTRICAL cmoUrr Robert M. Walker, Belmont, Mass, assignor, by mesne assignments, to the United States of America as represented by the Secretary of War Applicaticn August 1, 1945, Serial No. 608,304

6 Claims. 1

This invention relates in general to electrical circuits and more particularly to circuits for generating the sawtooth sweep voltages to be used with a cathode ray tube.

For most purposes the time base of an electrically-deflected cathode ray beam is a linearly increasing voltage with a fast return to a rest value. This requires that the voltage wave take the form of a sawtooth or serrated wave, its action being to move the spot formed by the impingement of the cathode ray beam on the face of a tube at a constant speed in one direction thereacross. An increase in linearity of the motion of this trace over that resulting from the use of a single sawtooth wave may be accompiished by using a push-pull sweep-generating circuit; i. e., one that applies sawtooth Wavefcrms'to both cathode ray tube deflection plates of one set, these waveforms being inverted with respect to each other.

Among the objects of this invention, therefore, are:

1. To provide a circuit for generating sawtooth voltage waveforms;

2. To provide such a circuitin which the sawtooth wave is substantially linear; and

3. To provide such a circuit having a pushpull output.

In accordance with the present invention there are provided two embodiments of a pushpull sawtooth wave sweep circuit. In the first embodiment a normally-conducting switch tube has an efiective capacitance connected between the plateof the tube and ground. A negative square pulse applied to the grid turns off the tube at the start of the development of the sawtooth wave. The voltage on the plate of this tube is coupled to a buffer tube and is then fed back through the cathode of this buffer to the plate load circuit of the switch tube. The output of the switch tube is also connected to an inverter tube through a capacitance voltage divider, the output of the inverter tube being one sawtooth Wave of the push-pull outputof the circuit. The other sawtooth wave of the pushpull output is taken from the cathode of the buffer tube.

In the second embodiment of the circuit a normally-conducting switch tube has a condenser connected between the plate and ground. A negative square pulse applied to the grid turns off the tube at the start of the development of the sawtooth wave. This plate is connected to the grid of a buffer tube. the cathode of which is connected back to a load resistor of the switch tube for feedback purposes. The cathode of the bufier tube is also connected through a capacity voltage divider to the grid of an inverter tube. One part of the push-pull sawtooth wave output is taken from the plate of the inverter tube, and the other part is taken from the cathode of the buffer tube.

This invention will best be understood by reference to the drawings, in which:

Fig. 1 shows one embodiment of my invention; and

Fig. 2 shows another embodiment of my invention. 1

Referring now to a description of the first embodiment of the circuit and to Fig. 1, it is seen that the input pulse is coupled to the grid 12 of switch tube 10 through coupling condenser II. The cathode [3 of tube 10 is grounded. Connecting the plate [4 of tube H) to the source of plate voltage, 3+, are two load resistors l5 and it. The grid l2 of switch tube It is returned to 13+ through grid-leak resistor II. -A

condenser I8 is placed between the plate M of' tube, It and ground. The plate M. of switch tube [0 is coupled t the grid 19 of buffer tube 20. The plate 2| of tube 23 is connected directly to 3+, and the cathode 22 of this tube is connected through a load resistor 23 to a source of negative voltage (-0) or to ground 24. The cathode 22 of tube is, connected back to the lower end of load resistor it through coupling condenser 32. One party of the push-pull output of the circuit, the so called positive sawtooth wave, is taken from the cathode 22 of the buffer tube 20.

The plate [4 of switch tube I0 is also coupled through condenser 25 to the grid 26 0f inverter tu e 2?. Grid leak resistor 28 connects the grid is cf this tube to ground. The plate 29 of tube 2? is connected through load resistor 30 to B+, and the cathode 3! of this tube is grounded. Feedback condenser 33 connects the plate 29 of tube 21 to the grid 26 of this tube. The other part of the push-pull output'of the circuit, the socalled negative sawtooth wave, is taken from the plate of inverter tube 21. I

The negative sawtooth wave is coupled to one deflcction plate 35 of cathode ray tube 34; while the positive sawtooth wave is coupled to the other deflection plate 36 of this tube.

Referring now to 'a description of the second embodiment of the sweep circuit and to Fig. 2, it is seen that the input pulse is fed to grid 40 of switch tube 4| through coupling condenser 42. The cathode 43 of tube 4| is grounded, and the 3 plate 44 is connected to a source of positive voltage, 3+, through load resistors 45 and 46. The grid 40 of tube 4| is returned to 3+ through grid-leak resistor 41. A sweep condenser 48 is connected from the plate 44 to ground.

The plate 44 is coupled directly to the grid 49 of buffer tube 55.. The plate 5| of tube 5|! is connected directly to 3+, and the cathode 52 of tube 55 is connected through a load resistor 53 to a source of negative voltage 6|. The lower end of resistor 53 is connected to ground by condenser 54. The cathode 52 of tube 50 is connected back to the lower end ofv load resistor 46 through coupling condenser 55.

The cathode 52 of tube Wis alsoconnected through a parallel network of resistor 56 and condenser 51 to the grid 58 of inverter tube 59. The cathode 65 of tube 59 is connected to a source of negative potential 6|, which in turn is connected to another source of negative potential 62 through potentiometer- The plate 64 of tube 5.9 is connected toB through plate resistor 6.5. The grid 58 is connected to the center arm of potentiometer 53 through resistor 66., Feedback condenser ll! connects theplate 6.4 to. the grid 58, of this. tube.

The positive sawtooth output, which is coupled to one plate 61 of cathode ray tube 68, comes from the cathode 52 of bul -er tube. 5.0, whilethe negative sawtooth output. which is. coupled to the other plate 59 of the cathode ray tube 68, comes. from the platetllof inverter tube 59...

Referring now to the operation of the first. em,- bodiment of the circuit. and. to, Fig. 1, it is seen that, due tothe. positive, gridv return. of switch tube Hi, this tube'will, benormally highly conducting, and its plate potential Willbe. low. A negativerectangular puls is. applied to the grid of this, tube, cutting it, off. Immediately two parallel capacitances begin charging onebeing. condenser l8, and the other being the. series capacitance-of condenser, 25 and the ihput capaoitance of tube 21;. This. latter. valuejsgmade quite. large due to the condenser 33" from plat,e,2,9 t grid 26. Thus, neglecting-v the. eftlect or; the. feedback throughcondenser 3.2, the. platevoltage oftube iii would rise. exponentially,,as, soon, as the switch tubestopsconducting. Due to. the feedback con.- nection from thecathode 011111112020 to the lower endof resistor It. thisJatter. pointri'sesin potential at a. rate. comparable. with the. voltage rise at the plate.oi1tube-|.0... Theefifect of" this feedback is V to, cause a. substantially constant charging current to. flow'into the ahovementioned parallel capacitances and. SQMtocause a linear rise in voltage at thepljateoftube f. This will also cause a linear positive sawtooth to appear at. the cathode oif tube 210., waveform isapplied to one deflection plate 36 of the cathode ray tube 34.

The positive. sawtoothwave on the plate oftube Iii is applied to the of. tube 21" through a capacity voltagedivider of condenser 25 and the input capacitance of tube 2'|., Thisinput capacitance; is purposely increasedby makinguse of the Miller efiect; Thus, the capacitance from the grid of tube 21 to ground is equal to the plate,- to-grid capacitance, which isefiectively equal to the capacitance of condenser- 33-, multip lied by the factor (G+1'), where Gis the gain of tube 21. Thus if E0 is the instantaneous output plate voltage of tube l0, E1 is the instantaneous inputgrid voltage of tube 21, andthecapacitance 33 is equal to the capacitance 25 4 and the instantaneous voltage E2 appearing at the plate of tube 21 will be cathode follower is where p is the: amplification factor of the tube. Since tube 25 is acting as a cathode follower, the instantaneous voltage at cathode 22, which is the instantaneous positive sawtooth voltage, will be p/( -i-l) times the voltage at the plate of tube It}. The negative sawtooth is taken from. the plate of tube 2.1, and the voltage at this point at. any instant is G/'(lG'.+2'-) times the voltage. on the plate of tube Ii). Thus, itcanbe seen that. the positive. and. negative sawtooth. voltages. are approximat y equ Referring now to the. operation of the circuit of. Fig. 2, it. is seen that normallyeconducting switch tube4| is switched. offi bythe negative rectangular pulse applied to the grid at which. time condenser 48. beginschargingt As in, the circuit. of Fig. I, this sawtooth waveform is .made. to be quite linear by co pling. the; plate of tube 4| to the grid of bulier tube 58;. and then, feeding. the voltage on the Cathodeofj tube. 55 backv to. the load circuit of tube 4|.

The sawtooth on the cathode of buffer tube 5!! is fed tothe grid of invert ir. tube. 59 through a compensated voltage divider... The. time constant of the resistance of resistor 55,mu1tiplied by the capacitance of condenser. 5.11s made sub.- stantially equal to the time constant of the resistance. of resistor 66: multiplied. by the input capacitance of tube 59, which isthe. capacitance of condenser 7,0. times. (G.+1) where, Gis the gain of tube 59. With thetwo. time constants being. equal, the ratio of the-voltage divider is made insensitive to frequency changes. In addition, the condenser 'lfl introducesnegative feedback for 3 5.91 and so. increases. the linearityand speed of starting of the sawtooth. wave. The positive sawtooth istakenfromthe, cathode of butler tube 5H,. while the negative sawtooth. is taken from the plate of inverter tube 531,

It will be. observedthat there isa d-.c path.

from the cathodeot tube, 50 to one deflection platev 61 of the cathode raytube, If-desired, sweep centering may: be obtainedby adjusting, the potentialof,v the cathode of tube. llwhichwillcontrol the potential.on'thecathode of. tuber5il. Arr-- increase in. the p otential of the cathode of tube 4| will decrease the average potentialon the upper deflection. plate-.61 and increase the average fications as fall within-thetruespirit. andscope of the invention,

I claim:

1. A circuit for generatingvpiish-pull sawtooth a sweep voltages for a cathode ray-tube comprise. ing a switch tubeihaving a: load circuit, capacitance means connected between the plate of said switch tube and a point of reference potential; meansv for applying pulses from a source external to saidcircuit onto said switch tube, whereby said switch tube ismade impervious to current flow therethrough and a positive sawtooth-wave of voltage is generated at the plate thereof, a buffer stage comprising a cathode follower circuit, means coupling said positive sawtooth wave to the grid of said cathode followroircuiufirst condenser means coupling the, cathode of said cathodefollower circuit back to the load circuit of said switch tube, whereby the linearity of said positive sawtooth wave is increased over the linearity of an exponential wave, means coupling said positive sawtooth wave at the cathode of said buffer tube to a first deflection means of said cathode ray tube, an inverter tube, voltage divider means applying said positive sawtooth wave to the grid of said inverter tube, whereby a negative sawtooth wave is present on the plate of said inverter tube, and means applying said negative sawtooth wave to a second deflection means of said cathode ray tube.

second; condenser coupling. the cathode of said buffer tube back to said taplon the resistive load circuit of said'switch tube, whereby the linearity of said positive'sawtooth wave is increased over the linearity of the exponential wave which would appear at the plate of said switch tube in the absence ofsaidsecond condenser, an inverter tube, a first resistance'means connecting the cathode of said buiier tube, to the grid of said inverter tube, a third condenser means in parallel with said first resistance means, a second resistance means of said cathode ray tube, and means coupling the plate of said inverter tube to'a second 2. A circuit for generating push pull sawtooth V sweep voltages for a cathode ray tube comprising a switch tube having a resistive load circuit, a capacitance means connected between the plate of said switch tube and a point of reference potential, means for applying negative pulses from a source external to said circuit onto the grid of said switch tube, whereby said switch tube is made impervious to current flow therethrough and a positive sawtooth wave of voltage is generated at the plate thereof, a buffer cathode follower tube, means direct-coupling the plate of said switch tube to the grid of said buffer tube, a first condenser coupling the cathode of said cathode follower tube back to an intermediate point on the resistive load circuit of said switch tube, whereby the linearity of said positive sawtooth wave is increased over the linearity of the exponential wave which would occur at the plate of said switch tube in the absence of the :use of said first condenser, an inverter tube, a portion of said capacitance means coupling the plate of said switch tube to the grid of said inverter tube, a second condenser connecting the plate of said inverter tube to the grid of said inverter tube, whereby the input capacitance of said inverter tube is used with said portion of said coupling capacitance as a voltage divider, means coupling the plate of said inverter tube to a first deflection means of said cathode ray tube, and means coupling the cathode of said buffer tube to a second deflection means of said cathode ray tube, whereby push-pull sawtooth voltage waves are generated at the cathode of said buffer tube and at the plate of said inverter tube.

3. A circuit for generating push-pull sawtooth sweep voltage waves for a cathode ray tube comprising a switch tube having a resistive load with a tap at some intermediate point on said load, a first condenser connected from the plate of said switch tube to a first point of reference potential, means for applying negative pulses to the grid of said switch tube, whereby said switch tube is made impervious to current flow therethrough and a positive sawtooth wave of voltage is generated at the plate thereof, a buflfer cathode follower tube, means coupling the plate of said switch tube to the grid of said bufl'er tube, a

deflection means of said cathode ray tube, whereby push-pull sawtooth voltage waves are generated at the cathode of said buffer tube and at the plate of said inverter tube.

4. A circuit for generating push-pull sawtooth sweep voltages for a cathode ray tube comprising a switch tube having a resistive load circuit, a first condenser connected between the plate of said switch tube and a point of reference potential, means for applying'pulses to said switch tube, whereby said switch tube is made impervious to current flow therethrough and a positive sawtooth wave of voltage is generated at the plate thereof, a buffer cathode follower tube,

ponential wave which would appear at the plate of said switch tube in the absence of said second condenser, an inverter tube, means coupling the cathode of said buffer tube to the grid of said inverter tube, means coupling the cathode of said buffer tube to a first deflection means of said cathode ray tube, and means coupling the plate of said inverter tube to a second deflection means of said cathode ray tube, whereby push-pull sawtooth voltage waves are generated at the oathode of said buffer tube and at the plate of said inverter tube.

5. A circuit for generating push-pull sawtooth sweep voltages for a cathode ray tube comprising a switch tube having a load circuit, capacitance means connected between the plate of said switch tube and a point of reference potential, means for applying pulses from a source external to said circuit onto said switch tube, whereby said switch tube is made impervious to current flow therethrough and a positive sawtooth wave of voltage is generated at the plate thereof, a buffer and inverter stage comprising a cathode follower buffer circuit and a plate inverter circuit, means coupling said positive sawtooth wave to control the current in said cathode follower buffer circuit and said plate inverter circuit, condenser means coupling the cathode of said cathode follower circuit back to the load circuit of said switch tube, whereby the linearity of said positive sawtooth wave is increased over the linearity of an exponential wave, means coupling the positive sawtooth wave at the cathode of said buffer circult to a first defieetibn meanss of'saiaeathode. my tube, and meanseouplmg the inverfiedasawtuoth; wave at the plateof. Sam-- inverter circuit-te msecond deflection means ef:.sa;idrcathede:ray: tube;

6. A circuit for generating'pusmpull; sawtuem sweep voltagee for aaeat'hod'e rayi tubewebmpmme: a switch tube Havmg'e; resistiveleaai elr'euic; afirst condenser eon-neeted: between: the place 6f said switch tube and a paint-i ofreietehee peten bememe" m ROBERT M. WALKER.

REFERENCES CITED The fdiiowing'. references are or record in the late inverter circuit; mezm cou ling the'pIabe of I said sW-ib'ch tube to control the current 1H said circuits, a second condenser eeup'nngtheeathcdeof said cet'hode folldw'ef'cifmt Back to them-ad circuit or said'switcri-t'ube; whereby the lifi'xiii? UNITED'STATES PATENTS m new. Schradef' May 30, 1944 

